Radio-frequency transmission through grounded conducting structures and the like



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0 62 0 Wdlgk' 3 Sheets-Sheet 1 K. L. BELL RADIO-FREQUENCY TRANSMISSION THROUGH GROUNDED CONDUCTING STRUCTURES AND THE LIKE a A g W m U Ev m. P 3 k w m n M 0m 1 T M m WW 4 D 1 H Um m L7 N 5 R m a w 6m w W M 5 3M M m 3 May 10, 1949.

Filed Sept. 20, 194.4

K. L. BELL RADIO-FREQUENCY TRANSMISSION THROUGH GROUNDED CONDUCTING STRUCTURES AND THE LIKE 3 Sheets-Sheet 2 WHTEQ PIPE zceimL. Ben,

May 10, 1949. K. L. BELL 2,47

RADIO-FREQUENCY TRANSMISSION THROUGH GROUNDED CONDUCTING STRUCTURES AND THE LIKE Filed Sept. 20, 1944 3 Sheets-Sheet 5 69 *66 I 7 I I I v I i 6'38 P PE Patented May 10, 1949 TATES ATENT OFFICE Keith Lansing Bell, Washington, D. 0., assignor to Curtis E. McGhee Application September 20, 1944, Serial No. 554,984

RADIQ-F-REQUE THROUGH GHQ 15 Claims 1 mitter was not adapted to apply suficiently great radio-frequency energy to the pipe, and the receiver was not adapted to convert the signal derived from the pipe into a sufficiently powerful audible signal and to maintain noise to signal ratio within permissible limits.

The distribution to the general public in a given municipality oi entertainment, news, andother program material, as now generally performed through space paths, involves diificult problems of frequency allocation, and interference between stations. Efforts to broadcast programs throughout a municipality over the electriclight distribution system have, in practice, encountered serious difficulties because of intervening electrical encumbrances such as transformers, which dissipate most of the radio-frequency energy, and also because of isolating unitsinterposed to keep line voltage on thereceiving sets. The system which I provide avoids these difficulties.

An object of my invention is to provide a radiof-requency transmitter employing as a part of the oscillating circuit, a relatively massive conducting structure substantially at ground potential.

Another object of my invention is to provide a grounded conductor radio-frequency transmission system wherein the conductor is direct coupled to the transmitter output, and one side i the plate potential is applied to the grounded conductor.

Another object of my invention is to provide a radio-frequency transmission system employing buried water pipes or gas pipes or the like.

A further object of my invention is to provide a receiving unit for deriving from a buried water pipe a transmitted radio-frequency signal and to translate the same into an audible signal.

Still another object of my invention is toapply a signal to be transmitted between a buried. pipe and the grounded conductor of a commercial electric light distribution system.

Yet another object of my invention is. to apply to a railroad rail a modulated radio-frequency signal which is to be transmitted.

My invention-will be better understood by reference to the following specification and the accompanying drawings, wherein the same .characters of reference indicate corresponding elements, and wherein:

Figure 1 shows a transmitting stationarranged according to my invention, wherein modulated radio-frequency energy is applied .between spaced points in a buried water pipe.

Figure 2 shows a transmitting station similar to that of Fig. 1, wherein modulated radio-frequency energy is applied between a point on a buried water pipe and a point on a buried gas pipe.

Figure 3 shows a transmitting station similar to that of Fig. 1 wherein modulated radio-irequency energy is applied betweena point on a buried water pipe and the grounded line wire of a commercial power distribution circuit.

Figure 4 shows a transmitting station similar to that of Fig. 1 wherein modulated radio-frequency energy is applied between two spaced points on a railroad rail.

Figure 5 shows a transmitting station similar to that of Fig. 1 wherein modulated radio-frequency energy is applied between two spaced points on a buried water pipe, the pathto one said point from the transmitter comprisinga substantial length of an elevated conductor.

Figure 6 shows a modified form of transmitter circuit wherein a parallel connection through condensers to the oscillator and modulator is provided for matching.

Figure '7 shows a receiving station having an input stage comprising an: input coil and network connected for deriving signal voltage between two spaced connections on a water pipe.

Figure 8 shows amodif ed form of receiving station employing in the input stage a simplified network with grid resistor and condenser.

Figure 9 shows the application of my transmitter toa massive structure such. as the metal frameor hull of a craft such as a submarine, ship, or surface craft, such as highway vehicles, or metal aircraft.

My system provides for the distribution within a restricted territory of modulated radio-frequency signals in a controlled effective manner without encumbering space channels.

Referring to the drawings in detail, in Fig. 1, there is shown a radio-frequency transmitter having its output applied to two spaced points I and 2 on a water pipe P which will ordinarily be buried in the ground. The water pipe is of substantial size as usually employed in the water 3 distribution systems of municipalities, and massive relative to the size of the electrical conductors customarily used. Water pipe mains as laid in the street for distribution are ordinarily at least four inches in diameter, and are usually larger. Such water pipes are generally metallically connected to the network of larger water mains and smaller pipes which usually constitute the water distribution system of a municipality.

The transmitter consists of an oscillator T and a modulator M. The particular oscillator and modulator circuits shown in Fig. l are particularly adapted to the purpose here in view, but other known oscillator and modulator circuits may be employed. The oscillator tube 3 has cathode 4, grid 5, and plate 6. Between cathode 4 and grid 5 are connected resistor 9 and inductor 8 which is an R. F. choke. A condenser E is connected to grid 5 beyond inductor 8 and an in ductor I is connected between the other terminal of condenser 1 and negative plate voltage. Inductor Ill is shunted by a condenser 12, and has a mid-tap H which is connected to cathode The output plate connection from plate i3 comprises the inductor-condenser network l3, i l, l5, which controls the output and prevents a shortcircuit of the oscillator output in case the resistance between connecting pipe straps l and 2 is very low and also is used to match the oscillator impedance with the load.

Oscillator T is plate modulated by modulator M in the circuit shown. The modulator tube has cathode l3, grid l9, and plate it. The grid 89 is coupled to microphone H by microphone transformer 24 having windings 25 and 28, and battery 28 supplies energy to microphone H. The inc-du lator plate 20 is connected to pipe strap 2 through variable inductor 2! and through the condenserresistance network 22, 23. The modulator plate 20 is also cennected to positive plate voltage through choke 29. Connecting wire it is connected, through the circuit elements as described, to grid 5 of the oscillator tube, and through R. F. choke l! to cathode [8 of the modulator tube. Provision is thus made to adjust oscillator and modulator for best performance with the given load. Connecting wire l6 should be carefully and completely insulated from ground for safety purposes. Besides amplitude modulation, the carrier may be signal modulated by frequency modulation or phase modulation.

For the purpose of safety, the negative bus l6 and all conductors at negative potential must be thoroughly insulated.

The water pipe P is an integral part in series connection of the oscillator circuit.

It will be observed that impedance elements are connected in series in the output circuit of the oscillator to avoid the possibility of overloading the oscillator if in some particular instance the load of the pipe is unusually low.

On a water pipe, the connections A and 2 are usually made thirty to fifty feet apart. The water pipe is scraped clean, and connections 8 and 2 made by pipe straps. The oscillator may employ almost any radio frequency, from 20 kilocycles to 100 megacycles. In simple applications, the oscillator output may be about thirty watts.

Video signal modulation as well as audio signal modulation may be transmitted by my system.

In choosing a frequency, consideration must be given to the fact that at very high frequencies the losses are much greater from radiation into space, and at angular bends and connections in the conductor.

Ultra-high frequencies when used on my transmission system are not limited to the horizon range, which materially increases transmission distances.

If desired a power amplifier stage may be interposed in the oscillator output to apply more output energy to the pipe, or other load device.

A radio-frequency ammeter may be inserted at A in Fig. l in the output plate lead.

Besides a water pipe, both connections may be made to a gas pipe or other pipe, preferably buried in the ground.

Figure 2 shows an arrangement wherein the modulated radio-frequency signal is applied between one strap connection lll to a water pipe P, and another strap connection ii to a gas pipe G. Gas pipes as laid in the street for distribution are usually at least two inches in diameter. The oscillator and modulator circuits are the same as those shown in Fig. 1. The arrangement with one connection to a water pipe and another connection to a gas pipe is found to work better in some localities, depending on the nature of the system of the underground pipe lay-out, and the kind of pipes available at the receiving station.

Figure 3 shows the application of the modulated radio-frequency signal between a water pipe P and the grounded wire 32 of a commercial volt lighting distribution line 3!, 32, grounded on one side. The high wire is connected through entrance switch 36 by wire 35 to the meter loop. The grounded wire 32, grounded at 3-3, is connected through entrance switch 35 by wire 35 to the meter loop, and is also connected by wire 3? through inductor i8 and its tap 39 to the plate of the oscillator tube. In some localities better results have been obtained with such an arrangement.

Figure 4 shows the application of modulated radio-frequency signal energy between two spaced points t2 and 53 on a railroad rail R. The oscillator and modulator circuits and impedance matchers are the same as are shown in Fig. l. The railroad rail is ordinarily in frequent contact with the ground. Radio-frequency signals may be transmitted over such a rail in this manner for long distances. Two rails, with crossconnections, may be employed. Improved transmission is obtained if adjacent rails are bonded.

Figure 5 shows the application of modulated radio-frequency energy between two spaced point 52 and 53 on a water pipe P through an elevated conductor ll in the nature of an antenna and a down lead 5i connected to strap 53 on pipe P. The output of the oscillator tube is connected through a variable inductor A l to a point 46 near one end of the elevated conductor ll. The plate of the modulator tube is connected through inductor 2i and wire 55 to the other strap 52 on pipe P. Elevated conductor ll is supported from towers or the like 48, 39, from which it is insulated by insulators 5t, 5Q-a. This arrangement has been found to improve transmission especially at the higher frequencies, by supplementing transmission through the buried conductor by space radiation from the elevated conductor; in some set-ups and localities this gives very good signals. This is particularly suited for the ultra-high frequencies required for video signals.

Figure 6 shows a modified form of modulating circuit wherein the modulator tube output is connected in parallel with the oscillator tube output. The oscillator plate is connected at point 5'! through wire 53 and inductor 59 to strap l at one point on pipe P, and is also connected from point 5'? through variable condenser 55 and point 56 and variable inductor Z! to strap 2 at the second point on pipe P. The plate of the modulator tube is connected through the parallel net of condenser 22 and resistor 23 to point 56. For some kinds of service, this arrangement gives best results. This is an alternative manner of matching the transmitter output impedance to a load impedance.

In the case of the application of the modulated radio-frequency signal energy to spaced points on the various kinds of massive conductors described, whether water pipes, gas pipes, the grounded side of an electric light line with its connecting grounded structures, or a railroad rail, or otherwise, I find that signal energy may be received at remote points of the systems embodying such massive conductors, and may be received and amplified and detected in usual manner. However, I find that certain particular arrangements are best suited to derive the radiofrequency signal from the massive conductor system, and apply it to the input stage of a receiving set.

One receiving arrangement is shown in Fig, 7. Water pipe P is provided with two spaced strap connections GE) and 6E. These connections are spaced 5 to 50 feet apart, depending on frequency and location. These straps are respectively connected by wires 1'2 and 73 to input coils l8 and H which are a split coil, that is, two coils wound on the same form and in mutual inductive relation. Tube 62 is the first input stage of any suitable receiving set which may be a superheterodyne or tuned radio-frequency or any other suitable set to meet the particular conditions. The signal grid 6 of the input tube 6'2 is connected through a suitable matching network of resistance 5?, condenser 68, and tuning condenser $9, to input coils 10, H.

The receiving system to the right of input tube 62 is conventional. The plate 65 of input tube 62 is shunted by condenser 65 and the output of this tube is connected through any suitable intervening stages indicated by dotted lines '14, T5, to the input grid 18 of the audio output tube 16, delivering audio signal to transducer 8!.

At the receiving station, the strap connections 60 and ES! could be applied, one to a water pipe and one to a gas pipe, or one to a water pipe and the other to the grounded line of a commercial electric light system, as shown for the transmitting station in Figs. 2 and 3.

For transmission over a railroad rail, as shown in Fig. 4:, the receiving connections 6t, 6!, would vated conductor at the receiving station being serially interposed in the connecting wire from either strap connection 6% or 5! in the circuit of either Fig. '7 or Fig. 8.

Figure 8 shows another kind of an input connection from a, gas pipe G, wherein the grid is connected only through a grid resistor 83 shunted by a grid condenser 82, to one strap 60 on pipe G, and the connection to the other strap BI is through inductor 85. This arrangement is better under some conditions.

Figure 9 shows another way of applying the system of my invention'to another kind .of massive conductor which may bein close electrical relation with the ground. The craft C shown in Fig. 9 may be a submarine, ship, surface craft such as an auto truck, tractor, or an armored tank. This principle may be applied to massive craft insulated from the ground, as metal aircraft fuselage, involving space radiation. The craft C is shown as having a massive metal hull or outer shell, and bow F and stern A. The oscillator and modulator circuits which are shown skeletonized, are substantially the same as those shown in Fig. 1. The plate Hit of oscillator tube 583 is shown as connected through impedance matching net lli'l, W8, mil, to the point IN on the hull or shell at the bow of craft C. The hull constitutes a serial portion of the output circuit of the oscillator. The plate lid of modulator tube IN is shown as connected through inductor MB to point 32 on the hull or shell at the stern ofcraft C. By suitable adjustment of the impedance matching units, a considerable amount of modulated radio-frequency signal energy may be applied to the medium of substantially ground potential in electrical relation with the hull or shell of craft C, and may be received and used at receiving stations in the vicinity which are in electrical relation with the medium at substantially ground potential. In receiving on craft, as shown in Fig. 9, the connections iii'i and 6! in the receivers of Figs. 7 or 8 are connected to bow and stern terminals W5 and H32 of the craft.

It is apparent that I have provided a substantial improvement in the transmission of news, entertainment and intelligence, over areas, such as municipalities, and that the system which I have disclosed has important advantages for this purpose.

It will be obvious to those skilled in the art that my invention is susceptible of various modiiications to adapt it to particular conditions and all such modifications which are within the scope of the appended claims I consider to be comprehended within the spirit of my invention.

I claim:

1. In a system for transmitting modulated radio-frequency energy, extended massive conductor structure means of dimensions much greater than are normally employed for transmitting radio-frequency communication currents, said massive conductor means being positioned in close electrical relation to ground, and a radio-frequenc transmitter comprising an os-- cillator, said oscillator including a prime source generating radio-frequency alternating voltage and delivering the same across primary output electrodes thereof, the output circuit of said oscillator being directly conductively connected to said primary output electrodes and comprising a substantial length of said massive conductor means which constitutes a substantially pure resistance path.

2. In a system for transmitting modulated radio-frequency energy, a radio-frequency transmitting station, a receiving station remote from said transmitting station, an extended length of relatively massive conducting structure means in close electrical relation with the ground, said transmitting station comprising a radio-frequency oscillator, said oscillator including a prime source generating radio-frequency alternating voltage and delivering the same across primary output electrodes thereof, the output circuit of said oscillator being'directly conductively connected to said primary output electrodes and comprising as a serial portion thereof a substantial length of said conducting means between substantially spaced points thereof which constitutes a substantially pure resistance path, and said receiving station having an input circuit which comprises a substantial length of said conducting means between substantially spaced points thereof.

3. In a system for transmitting modulated radio-frequency energy, a first relatively long metallic element buried in the ground, constituting a substantially pure resistance path, a second relatively long metallic element buried in the ground and spaced from said first element, a radio-frequency transmitter comprising an oscillator, said oscillator including a prime source generating radio-frequency alternating voltage and delivering the same across primary output electrodes thereof, a connection from a first said primary output electrode of said oscillator to a point on said first element, and a connection from a second said primary output electrode of said oscillator to a point on said second element.

4. In a system for transmitting modulated radio-frequency energy, an extended length of relatively massive conducting structure means in close electrical relation with the ground, a radiofrequency transmitter comprising an oscillator, said oscillator including a prime source generating radio-frequency alternating voltage and delivering the same across primary output electrodes thereof, the output circuit of said oscillator being directly conductively connected to said primary output electrodes and comprising a substantial length of said massive structure means which constitutes a substantially pure resistance path, and impedance matching means interposed in the output circuit of said oscillator for matchin the output impedance of said oscillator with the connected load impedance.

5. In a system for transmitting modulated radio-frequency energy, extended massive conductor structure means of dimensions much greater than are normally employed for transmitting radio-frequency communication currents, said massive conductor means being positioned in close electrical ralation to ground, a radiofrequency transmitter comprising a tube oscillator having cathode, grid, and plate, a source of plate potential therefor, and substantially spaced load connections to said massive conductor means, the length of said conductor means between said load connections constituting a substantially pure resistance path, the output circuit of said oscillator being conductively connected to said plate and cathode and comprising as a serial portion thereof the length of said massive conductor means between said load connections, and the positive terminal of said source of plate potential being connected to one of said load connections by a conductive path, whereby positive potential is applied to said massive conductor means.

6. In a system for transmitting modulated radio-frequency energy, extended massive conductor means of dimensions much greater than are usually employed for transmitting radiofrequency communication currents, said massive conductor means being positioned in close electrical relation to ground, a radio-frequency transmitter comprising an oscillator, a source of plate potential therefor, and substantially spaced load connections to said massive conductor means, the length of said conductor means between said load connections constituting'a substantially pure resistance path, the output circuit of said oscillator comprising the length of said massive conductor means between said load connections, the positive terminal of said source of plate potential being connected to one of said load connections by a conductive path, and the negative terminal of said source of plate potential being completely isolated as to the existence of a conducting path from said massive conductor means.

'7. In a system for transmitting modulated radio-frequency energy, a transmitting station, a receiving station remote from said transmitting station, an extended length of metallic rail laid along the surface of the ground, said transmitting station comprising an oscillator, said oscillator including a prime source generating radio-frequency alternating voitage and delivering the same across primary output electrodes thereof, the output circuit of said oscillator being directly conductively connected to said primary output electrodes and comprising as a serial portion thereof a substantial length of said rail between substantially spaced points thereof which constitutes a substantially pure resistance path, and said receiving station having an input circuit which comprises a substantial length of said rail between substantially spaced points thereof.

8. In a system for transmitting modulated radio-frequency energy, extended massive conductor structure means of dimensions much greater than are normally employed for transmitting radio-frequency communication currents, said massive conductor means being positioned in close electrical relation to ground, and a modulated radio-frequency transmitter comprising an oscillator tube and a modulator tube, each of said tubes having a cathode electrode, a grid electrode, and a plate electrode, and a conductive connection between the plate electrode of said modulator tube and an electrode of said oscillator tube for modulating the output of said modulator tube, said conductive connection comprising a substantial length of said conductor means between substantially spaced points thereof constituting a substantially pure resistance path.

9. In a system for transmitting modulated radio-frequency energy, extended massive conductor structure means of dimensions much greater than are normally employed for transmitting radio-frequency communication currents, said massive conductor means being positioned in close electrical relation to ground, and a modulated radio-frequency transmitter comprising an oscillator tube and a modulator tube, each of said tubes having cathode, grid, and plate, and a conductive connection between the plates of said tubes comprising a substantial length of said conductor means between substantially spaced points thereof constituting a substantially pure resistance path.

10. In a system for transmitting modulated radio-frequency energy, extended massive conductor structure means of dimensions much greater than are normally employed for transmitting radio-frequency communication currents, said massive conductor means being positioned in close electrical relation to ground, and a modulated radio-frequency transmitter comprising an oscillator tube and a modulator tube, each of said tubes having cathode, grid, and plate, and a conductive connection between the plates of said tubes comprising as a serial portion thereof a substantial length of said conductor means between substantially spaced points thereof constituting a, substantially pure resistance path.

11. In a system for transmitting modulated radio-frequency energy, extended massive conductor structure means of dimensions much greater than are normally employed for transmitting radio-frequency communication currents, said massive conductor means being positioned in close electrical relation to ground, and a modulated radio-frequency transmitter comprising an oscillator tube and a modulator tube, each of said tubes having cathode, grid, and plate, and a conductive connection between the plates of said tubes comprising a substantial length of said conductor means between substantially spaced points thereof constituting a substantially pure resistance path, and a source of plate potential having its positive terminal connected to said connection between said plates.

12. In a system for transmitting modulated radio-frequency energy, extended massive conductor structure means of dimensions much greater than are normally employed for transmitting radio-frequency communication currents, said massive conductor means being positioned in close relation to ground, a modulated radio-frequency transmitter comprising an oscillator tube and a, modulator tube, each of said tubes having cathode, grid, and plate, a source of plate potential having its negative terminal conductively connected to said cathode, a pair of substantially spaced electrical connecting means on said conductor means spaced along its length, the length of said conductor means between said connecting means constituting a substantially pure resistance path, a conductive connection from the positive terminal of said source of plate potential to a first one of said connecting means, a conductive connection from the second one of said connecting means to the plate of said oscillator tube, and a conductive connection between said first connecting means and the plate of said modulator tube, whereby the positive plate voltage of said oscillator tube is applied to its plate serially through a substantial length of said conductor means.

13. In a system for transmitting modulated radio-frequency energy, extended massive conductor structure means of dimensions much greater than are normally employed for transmitting radio-frequency communication currents, said massive conductor means being positioned in close electrical relation to ground, a modulated radio-frequency transmitter comprising an oscillator tube and a modulator tube, each of said tubes having cathode, grid, and plate, a source of plate potential having its negative terminal conductively connected to said cathodes, a pair of substantially spaced electrical connecting means on said conductor means spaced along its length, the length of said conductor means between said connecting means constituting a substantially pure resistance path, a conductive connection from the positive terminal of said source of plate potential to a first one of said connecting means, a conductive connection from the second one of said connecting means to the plate of said oscillator tube, a conductive connection between said first connecting means and the plate of said modulator tube, and the negative terminal of said source of plate potential being completely isolated as to the existence of a conducting path from said massive conductor means, whereby the positive plate voltage of said oscillator tube is applied to its plate serially through a substantial length of said conductor means.

14:. In a system for transmitting modulated radio-frequency energy, an extended length of metallic pipe of substantial diameter positioned in close electrical relation to ground, a modulated radio-frequency transmitter comprising an oscillator tube and a modulator tube, each of said tubes having cathode, grid, and plate, a source of plate potential having its negative terminal conductively connected to said cathodes, a pair of electrical connecting means on said pipe substantially spaced along its length, the length of said pipe between said connecting means constituting a substantially pure resistance path, a conductive connection from the positive terminal of said source of plate potential to a first one of said connecting means, a conductive connection from the second one of said connecting means to the plate of said oscillator tube, a conductive connection between said first connecting means and the plate of said modulator tube, and the negative terminal of said source of plate potential being completely isolated as to the existence of a conducting path from said pipe, whereby the positive plate voltage of said oscillator tube is applied to its plate serially through a substantial length of said pipe.

15. In a system for transmitting modulated radio-frequency energy, a length of metallic pipe carrying modulated radio-frequency current, said pipe being buried in the ground, a pair of connecting means electrically connected to said pipe at substantially spaced points thereof, the length of said pipe between said connecting means constituting a substantially pure resistance path, a receiving station comprising an input tube having cathode, grid, and plate, a pair of input windings in mutual inductive relation, a conductive connection from a first one of said connecting means to a, first terminal of a first one of said windings, a conductive connection from the second one of said connecting means to a first terminal of the second one of said windings, a connection from the second terminal of the first one of said windings to the grid of said input tube, and a connection from the second terminal of the second Eng of said windings to the cathode of said input KEITH LANSING BELL.

REFERENCES CITED I'lie following references are of record in the file of this patent: 

